Hormone therapy is giving the body hormones to increase or add certain qualities associated with a sex, these hormones guide your body on how to gain the attributes of the sex the hormone belongs to. Female hormones given to a male would result in:
• Growing breasts, as well as fat moving to face and hips/thighs
• Losing muscle tone and sweating less
• Thining of chest hair and facial hair and expansion of pelvis
• Smaller and fewer erections
• Shrinkage of testicles and severe slow down or halt of sperm production
Hormone therapy on a female (in a transgender attempt) results in essentially the opposite of what happens to a male in terms of physical appearance, and they too lose some significant level, if not all, of their fertility.
Physical appearance does not determine the sex. Fat/hair in certain areas, size of breasts and skeletal shape are byproducts of the sex (necessary for survival or not), not the sex itself.
Presence of fertility does not determine the sex. Mr Smiles, the trans supporter himself admitted that the lack of fertility of a women doesn't deprive her of being female, Mr Smiles's own argument destroys the possibility of the presence of fertility being sex determinative.
This argument lacks any reason whatsoever to believe that physical appearences are sex dererminative and will have to outrule the thousands of examples of people who have physical appearance disorders but are still their original gender, this argument ultimately fails.